This invention relates to a method for controlling preferably an electro-hydraulic automatic transmission of a motor vehicle specially fitted with a combustion engine, while the combustion engine can be influenced via control elements, preferably an accelerator pedal or a throttle valve, and gear levels of a transmission are shifted via shifting parameters which, at least as a function of the throttle valve position, the traveling speed and motor speed, are shifted automatically.
Common automotive transmissions of motor vehicles powered by combustion engines initiate, as a rule, an upshift (reduction of the speed ratio) when releasing the accelerator pedal. This, however, is not always desirable when driving around bends, because this type of change of load may possibly result in unsafe driving conditions or, when reaccelerating the vehicle by stepping on the gas, it is necessary to force one or several kick-downs (increase in the speed ratio).
From DE 33 41 652 C2, (having corresponding U.S. counterpart U.S. Pat. No. 4,679,145) it has become common knowledge that this type of upshifting in bends can be avoided through recording the transverse acceleration of the vehicle. However, by these means, one would merely avoid upshifting in bends.
In order to be able to avoid upshifting as soon as the vehicle approaches a bend, during the method of controlling an automatic transmission according to DE 39 22 040 A1, the change of speed effected by the accelerator pedal is recorded and by dropping below a specific (negative) limiting value, a signal preventing the upshifting is transmitted if a shearing action is detected. As a result, upshifting is prevented until the tensile action occurs and a fixed interval has passed.
DE 39 22 040 A1 (having corresponding U.S. counterpart U.S. Pat. No. 5,157,609) also provides that this interval is a function of an additional parameter (driving activity), which is derived from a multitude of operating or driving parameters of a motor vehicle and evaluates the driver's style of driving or a momentarily existing traffic situation.
In view of the state-of-the-art referred to in the foregoing, it is the object of the present invention to create a method for controlling an automatic transmission of a motor vehicle, which is improved further with respect to shift performance during braking, especially before entering bends.
The foregoing object is achieved in the present invention by the characteristic features that a gradual kick-down (increase in the gear ratio) occurs when a service brake of the vehicle is engaged, or alternatively in addition or supplementary thereto, the time variation of the traveling speed is less than a first negative longitudinal acceleration limiting value; and the transversal acceleration recorded by the transversal acceleration sensor lies below a first traveling speed-dependent transversal acceleration limit; and the time variation of the traveling speed is higher than a second negative longitudinal acceleration limiting value; and the traveling speed is less than a second traveling speed acceleration limiting value. Further characteristics as a development of the invention are described herein.
The advantages of the invention are primarily that a method for controlling an automatic transmission of a motor vehicle has been created, in which the shifting performance during braking, in particular before entering bends, has been improved further.
When reducing a vehicle's speed by braking, automatic kick-downs can be executed under certain conditions; the maintaining of conditions ensures a safe operation of the vehicle. The method especially ensures that the transversal acceleration is not too high, the vehicle's deceleration is not too great and the traveling speed is not too high, so as to avoid a loss, especially in the longitudinal and lateral stability of the wheels of the vehicle.
The brake torque of the driving (combustion) motor, which after kick-down has a stronger effect on the drive gears, can therefore not have a negative effect on the driving performance of the vehicle. In this case, kick-down occurs gradually, always by an interposition of a specific interval.
Kick-down while braking is preferably initiated when an upshift prevention condition is active. This is activated by a known method when the vehicle approaches a bend and the driver releases the accelerator pedal relatively fast.
On the one hand, by performing kick-downs during braking, the braking action of the vehicle's prime mover is intensified when in shearing action, so that the brakes (service brake) of the vehicle are relieved. On the other hand, in connection with maintaining the speed before, in the course of and after driving the bend, the driver, after passing through the bend, can always operate at the optimal gear level to reaccelerate the vehicle.
In the following, the invention is explained in greater detail by means of the drawing and particular embodiments.